The invention relates to a servo-assisted rack-and-pinion steering system having a helical-toothed rack and a helical-toothed pinion cooperating therewith.
A rack-and-pinion steering system is known, for example, from German Patent document DE 41 26 020 A1. The helical toothing of the rack serves, on the one hand, to ensure that the transmission of forces between the pinion and the rack is jerk free. On the other hand, the forces occurring between the toothings are utilized for displacing the pinion, which is axially mounted in a resilient manner, in one direction or the other in dependence on the direction of rotation. This displacement is then utilized to control a servo valve arrangement for a hydraulic servomotor assisting the steering system. A basically similar arrangement is the subject of EP 01 92 641 B1.
In rack-and-pinion steering systems of the type indicated above, it is known from German Patent document DE 42 03 335 A1 to mount the pinion so as to be swivellable. The side of the pinion which is connected to the steering shaft is mounted in a fixed bearing and the other side is mounted in a floating bearing. When the forces are transmitted between the pinion and the rack, the swivelling movement of the pinion in one direction or the other, which occurs through constraint, is here then utilized to control servo valves of a hydraulic servomotor.
In principle, the servo valves can also be controlled if the pinion has a fixed axial and radial mounting.
It is, for example, known from German Patent document DE 30 43 968 C2 to construct the steering shaft with parts which are capable of limited rotation relative to one another. The relative rotation of these parts is used to control the valves.
In the case of mass produced motor vehicles, the steering shaft parts rotatable relative to one another often form a rotary slide valve by which the hydraulic servomotor can be controlled.
There is therefore needed a form of servomotor control which is particularly suitable for rack-and-pinion steering systems.
According to the present invention, this need is met in that rotary movements of the rack, which is capable of limited rotation relative to its longitudinal axis, serve to actuate control elements of the servomotor.
The present invention is based on the realization that, in the transmission of forces between the pinion and the rack, a torque is exerted on the rack because of the helical toothing. The direction of the torque is dependent on the direction of rotation of the pinion.
This rotary movement of the rack is unavoidable in rack-and-pinion steering systems because, to avoid toothing play, the rack is resiliently pressed against the pinion and, accordingly, can also yield by rotation to the pressure applied by spring action.
For the purpose of implementing the present invention, it is thus possible to use basically unchanged designed conventionally rack-and-pinion steering systems. It simply is necessary for elements to be provided which are moved by or together with the rack and which make a movement stroke analogous to the rotary movement of the rack.
According to a preferred embodiment of the present invention, a lever is provided which is coupled to the rack and is arranged radially in relation to the rack and which swivels in correspondence with the rotation of the rack.
The arrangement is preferably such that the lever is able to be displaced, relative to the rack, in the longitudinal direction of the rack and, accordingly, does not need to participate in the displacement movements of the rack.
A particular advantage of the present invention is that the rack is able to make comparatively pronounced swivelling movements, so that the servomotor can, without difficulty, be controlled by long adjustment strokes.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.